1. Field of the Invention
The present invention relates to a surface planarization apparatus for polishing a workpiece in its pressed state by a rotating surface plate and also to a workpiece measuring method.
2. Description of the Related Art
Conventionally, a chemical and mechanical polishing (hereinafter simply referred to as CMP) apparatus has been known as such a kind of surface planarization apparatus.
FIG. 13 shows in cross section an example of a CMP apparatus. In FIG. 13, a reference symbol 100 designates a surface plate which is formed of a disk member with a polishing pad 101 made of urethane being adhered to an upper surface thereof. The surface plate 100 is mounted on an upper surface of a rotation member or rotor 100 which in turn is rotatably mounted on a central shaft 111 through a bearing 112. By energizing a drive means 130 such as a motor to rotate the rotor 110, the surface plate 100 is caused to rotate together with the rotor 110.
With this CMP apparatus, a work 200 disposed on the surface plate 100 is urged or pressed against the surface plate 100 by means of a carrier 210 so that it is driven to rotate so as to be planarized or polished by the surface plate 100 while a polishing medium such as a polishing liquid is supplied thereto.
Specifically, the workpiece 200 is pressed against the surface plate 100 through a packing pad 211 to a lower surface of which the carrier 210 is adhered. In this state, the surface plate 100 and the carrier 210 are caused to rotate in the right-hand or clockwise rotational direction at the same rotation speed. At this time, the carrier 210 is oscillated in a radial direction of the surface plate 100, as shown by an arrow A.
Furthermore,, the CMP apparatus is provided with a laser sensor 300 for measuring the state of planarization or polishing of the workpiece 200.
Specifically, a small-diameter hole 120 is formed through the polishing pad 101, the surface plate 100 and the rotor 110 with the laser sensor 300 being disposed under the hole 120.
With this arrangement, when the hole 120 comes right above the laser sensor 300 during rotation of the surface plate 100, a laser beam is issued from the laser sensor 300 toward the hole 120 to thereby measure the polishing state of the workpiece 200 over the hole 120.
However, the rotating surface plate of the above-mentioned polishing apparatus has involved the following problems.
During continued use of the polishing pad 101, the central portion of the polishing pad 101 is worn out greater than the inner and peripheral portions thereof.
That is, the polishing pad 101 has been frequently subjected to a localized or non-uniform wear, and the operation of the CMP apparatus has to be stopped every time such a localized wear takes place, so that the polishing pad 101 is dressed, cutting down the inner and outer peripheral portions up to the thickness of the central portion to thereby level the entire surface of the pad. Otherwise, the polishing pad 101 thus locally worn has to be replaced with a new one. As a consequence, it is necessary to stop the CMP apparatus for a long period of time, and hence the operating rate of the apparatus is very bad.
Moreover, since when the rotating hole 120 comes right above the laser sensor 300, it is necessary to operate the laser sensor 300, the control of timing is very difficult. Especially, since the workpiece 200 is swung or oscillated in a radial direction of the surface plate 100, the oscillating movement of the carrier 210 need be controlled to locate the central and peripheral portions of the workpiece 200 just above the hole 120 when the hole 120 comes right above the laser sensor 300. Thus, such a control is very difficult. As a consequence, the polishing state of the workpiece 200 can not be measured accurately.
Furthermore, the laser measurement has sometimes been disabled or obstructed due to the polishing liquid collected in the small hole 120. In addition, measurements are limited to only the central portion and a part of the peripheral portion of the workpiece 200.
The present invention is intended to solve the above-described various problems based on the following consideration.
The invention have noted a difference between the length of sliding contact of the polishing pad 101 with the work 200 when the workpiece 200 is located at an outermost peripheral portion of the polishing pad 101 and the length of sliding contact thereof when the workpiece 200 is located at an innermost peripheral portion of the polishing pad 101.
FIG. 14 is a schematic plan view showing an oscillating state of the workpiece 200. FIG. 15 is a comparison chart in which sliding contact lines in FIG. 14 are superposed for the purpose of comparison.
When the surface plate 100 is located at the outermost peripheral portion of the polishing pad 101 due to a swinging of oscillating motion thereof in the direction of arrow A as shown in FIG. 14, a sliding contact line 3 indicated at an alternate long and short dash line is taken, whereas when the surface plate 100 is located at the innermost peripheral portion of the polishing pad 101, a sliding contact line C indicated at a short dashes line is taken.
The length of the sliding contact line B increases from the left-hand end of the workpiece 200 to the central portion thereof and decreases from the central portion toward the right-hand end of the workpiece 200. The length of the sliding contact line C changes similarly, too.
However, as shown in FIG. 15, the lengths of the sliding contact lines B and C of the corresponding portions of the workpiece 200 vary according to the position of the work 200. For instance, when a comparison is made between a leftmost sliding contact line B' when the workpiece 200 is at an outermost peripheral position and a sliding contact line C' when the workpiece 200 is at an innermost peripheral position, the sliding contact line C' is longer than the sliding contact line B'.
In order to analyze this phenomenon, the inventors took the length of a sliding contact line as the corresponding time of sliding contact, and considered the sliding contact time at each position of the workpiece 200.
FIG. 16 schematically illustrates in a plan view the position of oscillation or swing of the workpiece 200, and FIG. 17 is a diagram illustrating the sliding contact time in which the left-hand ordinate axis indicates the sliding contact time at each position and the right-hand axis ordinate indicates the value of time at which the sliding contact times of respective positions are superposed one over another.
First of all, when a workpiece 200-1 is disposed at a location P1 in FIG. 16 (e.g., 162 mm apart from the center O of the polishing pad 101), the sliding contact time of the polishing pad 101 during which it contacts the workpiece 200-1 takes a curve S1.
That is, the sliding contact time is 0 seconds at the opposite ends of the workpiece 200-1, and it takes a maximum value of about 0.45 seconds substantially at the center of the workpiece 200-1. Subsequently, when another workpiece 200-2 is disposed at a location P2 which, in this embodiment, is 171 mm apart from the center O of the polishing pad 101, there is obtained a curve S2 having a maximum value of 0.42 seconds.
In this manner, when workpiece 200-3 through 200-6 were disposed at locations P3 through P6 which are apart from the center O of the polishing pad 101 by distances of 180 mm, 189 mm, 198 mm, 207 mm, 216 mm, and 225 mm, respectively, the corresponding sliding contact times take curves S3 through S6.
As can be seen from these curves S1 through S6, the greater the distance of the workpiece 200 from the center O of the polishing pad 101 (i.e., as the workpiece 200 moves from the center O of the polishing pad 101 toward the outer periphery thereof), the maximum value and the curvature of the sliding contact time of each curve decreases.
Accordingly, as shown in FIG. 16, when the workpiece 200 (200-1 through 200-6) is swung or oscillated within the range of a distance L, the time during which the workpiece 200 is in sliding contact with the polishing pad 101 becomes equal to the time in which the curves S1 through S6 are superposed one over another. Superposition of the curves S1 through S6 provides a curve T having a maximum value of about 3 seconds. The curve T takes the shape of an arc which is gently sloping at the central portion thereof designated at a range M, and falls at the inner peripheral portion designated at a range R and the outer peripheral portion designated at a range N. Therefore, the polishing pad 101 is worn out violently in the range M, and lesser in the ranges R and N. As a result, the polishing pad 101 is worn out in the shape of an inverted curve T, resulting in a localized wear, as shown in FIG. 18.
In order to cope with such a localized wear, it is considered to use a polishing pad having a lesser or finer width or another one in the shape of a line ring.
Specifically, as shown in FIG. 17, the curve T is substantially horizontal in a limited range .DELTA. in the vicinity of the top of the curve T, so there will be caused no localized wear. Therefore, if a polishing pad 101 in the shape of a line ring and having a width of .DELTA. while passing through the top position of the curve T is driven to rotate with the workpiece 200 being caused to rotate and oscillate on the line-ring-shaped polishing pad 101, an ideal polishing can be achieved without generating any localized wear on the polishing pad 101. However, when the polishing pad 101 is formed into the line shape in this manner, the area of contact thereof with the workpiece 200 becomes small, thus decreasing the polishing rate.
Another measure to cope with the above problem is that the radius of the polishing pad 101 is made twice or more the diameter of workpiece 200, so that the surface of the polishing pad 101 which is in sliding contact with the workpiece 200 is always changed during swinging or oscillating motion of the workpiece 200.
However, it is not desirable in these days to provide such a large-sized CMP apparatus particular in view of the fact that miniaturization of a CMP apparatus is demanded.